Research On Hybrid Control Of Waveform Presetting And Liquid Bridge Status Feedback In Short Circuit Transfer Welding

As its low cost and high productivity, CO2gas shielded arc welding is widely used in low carbon steel and low alloy steel welding process. But short circuit transition, as an important kind of melting metal transition mode in CO2gas shielded arc welding, is accompanied by a large welding spatter loss coefficient which affecting the weld quality. In view of the low accuracy and narrow scope of application process in the existing spatter control method, hybrid control of waveform presetting and liquid bridge status feedback in short circuit transfer welding is studied in this thesis. It has very important theoretical meaning and practical value for the research and development of low spatter and high efficiency CO2short-circuit welding technology and equipment, and promoting our country’s welding steel structure manufacturing level.According to CO2short circuit transfer welding, using the virtual instrument LabVIEW an acquisition system is established. According to software delay which offsets the difference of starting delay time between data acquisition system and high speed camera, the function of synchronous acquisition for electrical parameters and molten droplet images is realized. The corresponding analysis software is designed for off-line analysis of the original current and voltage signals.Based on the comparison of each electric parameter signal in short circuit transfer welding process, respectively use the arc voltage and arc voltage derivation to characterize the occurrence of short circuit and critical necking of liquid bridge. And through the synchronous detection of the molten droplet images and electrical parameters, the characteristic values of the two critical statuses are calculated. Using measured characteristic values of the bridge status characterization parameter, the feedback control of CO2short circuit transfer welding is realized. By varying the shape of current waveform, the change law of each time parameter in short circuit transition process with different current waveform parameters is analyzed. From the angle of energy distribution in short circuit transition, the change law of weld forming with different current waveform parameters is analyzed too.Using orthogonal test of welding process, current waveform parameters in different wire feed rate are optimized. And the optimum matching relationship of peak current, base current and current tail drag is obtained. By calling the optimal current waveform parameters in welding process, hybrid control of waveform presetting and liquid bridge status feedback in short circuit transition welding is realized.